The "Can't contact LDAP server" error is usually returned when the LDAP server cannot be contacted. This may occur for many reasons:

the LDAP server is not running; this can be checked by running, for example,

telnet <host> <port>

replacing <host> and <port> with the hostname and the port the server is supposed to listen on.

the client has not been instructed to contact a running server; with OpenLDAP command-line tools this is accomplished by providing the -H switch, whose argument is a valid LDAP url corresponding to the interface the server is supposed to be listening on.